Abstarct: Underwater explosion phenomenon is noticeable about 90 years ago and specific research in the case began 70 years ago, when World War II began. Valuable strategies in naval battles in World War II, was the most important factors in the study of the underwater explosion. In the underwater explosion ,gas bubbles are formed. Due to the density difference between water and the products resulting from the explosion and the creation of thermal gradient, a pressure field is formed in the water that causes the formation of shock waves and consequently the secondary waves. Multiple cycles of expansion and contraction of the bubble and the pressure field and temperature gradient in the surrounding fluid, bubbles, loose motions, cramps and will transfer. In this research First,we discussed the physics phenomena of underwater explosion and described the exprimental Formulas of underwater explosion. The meshless method (smoothed particle hydrodynamics) among other numerical methods as a suitable tool, was used for analysis of underwater explosions. The smoothed particle hydrodynamics(SPH) in underwater explosion analysis was an capable and efficient evaluation method, with the aid of the computer program LS-Dyna the results achieved. SPH method was very powerful and efficient tool for solving the problems such as: 1 - underwater explosion of a pressurized core expansion phase and gaseous products (bubble). 2 - underwater blast wave effects from rigid obstacles. 3 -Analysis of bubble interaction with the free surface in underwater explosion phenomenon. 4 - Modelling of the underwater explosion in three-dimensional environments.